Mobile communication systems have a tendency toward a larger traffic amount of data communication, and services to be provided are becoming more sophisticated. Therefore, there has been an increasing demand for high-speed radio transmission.
A frequency band allocable to the mobile communication system is limited, and hence there are provided various kinds of schemes as a technique for realizing high-speed radio transmission while effectively utilizing frequencies. Examples thereof include multi-level modulation such as 16 quadrature amplitude modulation (QAM) or 64 QAM, and multiple input multiple output (MIMO) transmission. Further, high-speed transmission is more realizable as an available continuous bandwidth becomes larger, and hence the frequency bandwidth itself is an important factor for realizing high-speed transmission.
Carriers, which are operators of the mobile communication systems, are each allocated a predetermined frequency band. Each of the carriers uses the frequency band thus allocated, to thereby provide a plurality of mobile communication services in its own mobile communication system.
The following document discloses a technology of dynamically changing a bandwidth allocated to a subscriber unit based on a data transfer rate for the purpose of realizing high-speed transmission in a mobile communication system using a code division multiple access (CDMA) scheme.    [Patent document 1] Japanese National Publication of International Patent Application No. 2002-510447